Internal combustion engines may operate in a variety of combustion modes. One example mode is homogeneous charge compression ignition (HCCI), wherein an air and fuel mixture achieves a temperature where combustion occurs by autoignition without requiring a spark being performed by a sparking device. In some conditions, HCCI may have greater fuel efficiency and reduced NOx production compared to other combustion modes. However, combustion modes such as HCCI may be limited under some conditions, since a substantial amount of heat and pressure may be needed to produce combustion.
One approach to providing sufficient heat to achieve combustion is U.S. Pat. No. 6,295,973, wherein intake air is heated by heat exchangers connected to the exhaust manifold and/or engine coolant before mixing with fuel in the cylinder. However, the inventors herein have recognized a disadvantage with such an approach. Specifically, during some conditions, such as at lower engine loads and/or speeds, the engine exhaust may provide insufficient heat.
Another approach to achieving auto-ignition and controlling initial charge temperature adjusts hot residuals retained within the combustion chamber by controlling exhaust throttling to achieve increased cylinder temperature. However, the inventors herein have realized that such an approach, under some conditions, may result in additional pumping losses or may provide an insufficient amount of heat to attain autoignition.
In one approach, the above issues may be addressed by a system, comprising of an internal combustion engine having a combustion chamber with a piston located therein, an intake passage coupled to the combustion chamber, wherein the intake passage supplies intake air to the combustion chamber, an adjustable compressor arranged in the intake passage upstream of the combustion chamber, a throttle arranged in the intake passage upstream of the compressor, and a controller configured to operate the engine so that, at least under some conditions, the piston compresses an air and fuel mixture within the combustion chamber to attain substantial auto-ignition of the mixture; and to increase a boosting of the compressor to increase heating of the intake air, and to decrease the boosting to decrease heating of the intake air, while throttling the intake air with the throttle.
Thus, in one example, heating of the inducted intake air can be accomplished by first throttling the intake air and then heating the intake air with a compressor while restoring the intake air to approximately unthrottled, or other, conditions in the intake manifold. In this manner, a throttle and a compression device, such as powered by a variable geometry turbine turbocharger, can be operated synergistically to regulate intake air temperature and flow, which in turn can be used to achieve improved or extended HCCI operation. Further, in some embodiments, charge motion control valves and/or variable valve timing may be used as additional or alternative mechanisms to control the start and duration of combustion. In this manner, sufficient heating of the intake air may be achieved even when the engine is producing an insufficient amount of heat to otherwise sustain HCCI operation.
Further, still other advantages may be achieved. For example, by coordinating the operation of the throttling and boosting, it may be possible to vary the intake charge temperature to an appropriate level during auto-ignition operation to account for heat from other sources, such as a heat exchanger or due to residuals, without adversely affecting the total flow through the cylinders. In this way, a desired air-fuel ratio, for example, may be more accurate controlled.